The other day, I discovered footage of goslings swimming behind the great Austrian ethologist Konrad Lorenz rowing a boat. Konrad Lorenz completed doctorates in medicine and biology. This combination was common for anatomists of his time, because many pursued research in comparative anatomy of the animal kingdom in addition to teaching gross anatomy. The Professor of Anatomy at my alma mater, Professor Dr. Dr. Dietrich Starck, displayed an elephant heart preserved in a huge glass jar in his office and was known around the world for editing the Handbooks of Zoology. Peculiarly, Konrad Lorenz did not follow the traditional career of an anatomist, but was drawn to behavioral studies. I remember his astounding manipulations of animal behavior from my secondary school days. We were shown movies of his work that IWF distributed to schools on big reels of regular eight celluloid film. The movies were silent. Subtext was added. Sound would not have been of much help. The projector rattled incredibly loud. Its bulb heated the classroom to a sweat. Despite, we loved watching those movies.
In one of them, Lorenz showed us how goslings became fixated in their behavior onto the object they found near them first after they hatched, following it wherever it went. The behavior was known from other nidifugous birds like chickens. In nature, the first object is commonly the mother. Lorenz substituted the mother with himself, and the ducklings followed him instead. Elaborate features proved unnecessary. The goslings would also accept a moving ball or a stroller. Most importantly, the object had to be present within 13-16 hours after hatching. Beyond this critical period the goslings would not attach to the object. The process is known as imprinting. Imprinted geese would maintain the behavioral object fixation for many months. Lorenz concluded that although the stimulus releasing the behavior could vary, the stereotypical behavior itself was enacted instinctively and must be innate, because the hatchlings did not have the opportunity to learn the behavior from any one else. You may wish to see Lorenz in action here:
In the early 1980s, Henning Scheich and others provided evidence that the connections between nerve cells in the brain are particularly modified in imprinted birds as another example of brain plasticity. Guinea fowl were imprinted onto objects emitting tones of particular pitch. Using the autoradiographic deoxyglucose method of Sokoloff and others (1987) to image local metabolic brain activity, the authors showed pronounced nerve cell activation in the birds auditory forebrain related to the pitch of imprint. The findings suggest that lasting nerve cell connections develop during the critical period of imprinting, embedding a memory trace of the release stimulus for the behavior. The findings were published in the Proceedings of the National Academy of Sciences (Maier and Scheich, 1983). Subsequent work established that the density of protrusions on nerve cell processes, known as dendritic spines, diminished on a particular type of cell in one of the activated brain regions (Wallhäusser and Scheich, 1987). Excitatory endings from other nerve cells mainly terminate on dendritic spines. Therefore, selective pruning of excitatory nerve endings on specific nerve cells during the critical period may underlie imprinting-related brain activation.
Douglas Spalding described filial imprinting already in the 19th century, perhaps providing the earliest notion of a behavior dependent on a critical period during postnatal development. In his work, Konrad Lorenz elaborated on this notion, providing a foundation for Torsten Wiesel's and David Hubel's discovery of a critical period for plasticity of cerebral cortex. They discovered interlocked domains in visual cerebral cortex, in which nerve cells responded predominantly to the stimulation of either one eye. Because the dominance of monocular input spanned the cortical thickness, the domains are known as ocular dominance columns. Occlusion of one eye during the critical period resulted in the expansion of the columns receiving input from the unimpeded eye. The effect was reversible as long as the eye occlusion was switched during the critical period (Wiesel and Hubel, 1965). These findings laid the groundwork for the exploration of the nerve cell mechanisms involved in brain plasticity and behavior.
Lorenz shared the Nobel Prize with Niko Tinbergen and Karl von Frisch in 1973 and Wiesel and Hubel with Roger Sperry in 1981. I have written about Sperry's discoveries on split brains in my post dated Apr. 28, 2009.
- Konrad Lorenz's student Irenäus Eibl-Eibesfeldt used a camera lens with a mirror that permitted him to film the facial expressions of unsuspecting bystanders unnoticed. Taking pictures in this fashion, he and his colleagues were able to identify archetypal facial expressions commonly used across cultures, suggesting that also humans share innate behaviors. Eibl-Eibesfeldt authored an authoritative book on his observations entitled "Human Ethology". The raising of the eye brows to signal readiness for social interaction represents one example shown on the home page of the Film Archive of Human Ethology. (10/28/09).
- Eibl-Eibesfeldt I (1989) Human Ethology. DeGruyter, New York.
- Lorenz K (1978) Behind The Mirror: A Search for a Natural History of Human Knowledge. Harcourt, New York.
- Maier V, Scheich H (1983) Acoustic imprinting leads to differential 2-deoxy-D-glucose uptake in the chick forebrain. Proc Natl Acad Sci USA 80:3860-3864.
- Sokoloff L, Reivich M, Kennedy C, Des Rosiers MH, Patlak CS, Pettigrew KD, Sakurada O, Shinohara M (1977) The [14C]deoxyglucose method for the measurement of local cerebral glucose utilization: theory, procedure, and normal values in the conscious and anesthetized albino rat. J Neurochem 28:897-916.
- Wallhäusser E, Scheich H (1987) Auditory imprinting leads to differential 2-deoxyglucose uptake and dendritic spine loss in the chick rostral forebrain. Brain Res 428:29-44.
- Wiesel TN, Hubel DH (1965) Extent of recovery from the effects of visual deprivation in kittens. J Neurophysiol 28:1060-1072.